System and methods for efficient digitization in a communication network

ABSTRACT

An analog signal processor includes a sampling unit configured to (i) filter, in the frequency domain, a received time domain analog signal into a low-frequency end of a corresponding frequency spectrum, (ii) sample the filtered analog signal at a frequency substantially higher than the low-frequency end, and (iii) spread quantization noise over an expanded Nyquist zone of the corresponding frequency spectrum. The processor further includes a noise shaping unit configured to shape the spread quantization noise out of the low-frequency end of the corresponding frequency spectrum such that the filtered analog signal and the shaped quantization noise are substantially separated in the frequency domain, and a quantization unit configured to apply delta-sigma modulation to the filtered analog signal using at least one quantization bit, and output a digitized bit stream that substantially follows the amplitude of the received time domain analog signal.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/847,417, filed Dec. 19, 2017, which application claims the benefit ofand priority to U.S. Provisional Patent Application Ser. No. 62/435,961,filed Dec. 19, 2016, which is incorporated herein by reference in itsentirety.

BACKGROUND

The field of the disclosure relates generally to fiber communicationnetworks, and more particularly, to digitization techniques in hybridfiber coaxial networks.

Typical hybrid fiber-coaxial (HFC) architectures deploy few long fiberstrands from fiber a hub to a node, but often many short fiber strandsare deployed to cover the shorter distances that are typical from legacyHFC nodes to end users. Conventional Multiple Service Operators (MSOs)offer a variety of services, including analog/digital TV, video ondemand (VoD), telephony, and high speed data internet, over HFC networksthat utilize both optical fibers and coaxial cables.

FIG. 1 is a schematic illustration of a conventional HFC network 100operable to provide video, voice, and data services to subscribers. HFCnetwork 100 includes a master headend 102, a hub 104, a fiber node 106,and end users/subscribers 108. An optical fiber 110 carries opticalanalog signals and connects the link between master headend 102, hub104, and fiber node 106. A plurality of coaxial cables 112 carry radiofrequency (RF) modulated analog electrical signals and connect fibernode 106 to respective end users 108.

In operation, fiber node 106 converts the optical analog signals fromoptical fiber 110 into the RF modulated electrical signals, which arethen transported along coaxial cables 112 to end users/subscribers 108.In some instances, HFC network 100 implements a fiber deep architecture.HFC network 100 may further utilize electrical amplifiers 114respectively disposed along coaxial cables 112 to amplify the RF analogsignals to respective end users 108. In HFC network 100, both theoptical and electrical signals are in the analog form from hub 104 allthe way to the subscriber's home of end user 108. Typically, a cablemodem termination system (CMTS) is located at either headend 102 or hub104, and provides complementary functionality to cable modems (CMs) (notshown) respectively disposed at end users 108.

Recently, the Data Over Cable Service Interface Specification (DOCSIS)has been established as an international standard interface that permitsthe addition of high-bandwidth Internet protocol (IP) data transfer toan existing HFC network, such as HFC network 100. The latest DOCSISstandard, DOCSIS 3.1, offers (1) the opportunity to expand transmittedspectrum beyond the bandwidths that had previously been available, andin both the downstream and upstream directions, and (2) more efficientuse of the spectrum itself. However, a DOCSIS 3.1 HFC network (i.e.,supporting orthogonal frequency division multiplexing (OFDM)), whencompared with its previous DOCSIS HFC network counterpart, requiressignificantly higher system performance for both the upstream and thedownstream signals, and particularly with respect to the carrier tonoise ratio (CNR) or the modulation error ratio (MER).

The DOCSIS 3.1 Physical Layer Specification defines the downstreamminimum required CNR performance of OFDM signals with low-densityparity-check (LDPC) error correction in additive white Gaussian noise(AWGN) channel as shown in Table 1, below. For example, a typical OFDMquadrature amplitude modulation (QAM) of 1024 (1K-QAM) requires a signalperformance of 34 dB CNR, or approximately 41-41.5 decibels (dB) CNR forthe 4K-QAM modulation format option in the downstream direction. Asimilar situation occurs in the DOCSIS 3.1 upstream transmission path,as shown in Table 2, also below.

In such analog HFC systems, the quality of the recovered RF signalchannel (e.g., at CMs of end users 108) is determined according to thecarrier-to-composite noise (CCN), or CCN ratio. The CCN of an HFC fiberlink represents the combination of noise components (e.g., shot noise,thermal noise, laser noise (i.e., from hub/headend laser transmission),etc.), the intermodulation noise (e.g., second, third, and higher ordercomponents), and the crosstalk noise (e.g., nonlinear fiberinteractions, such as four-wave mixing, cross-phase modulation, Ramancrosstalk, etc.). Continuous envelope and high peak-to-average powerratio (PAPR) are significant concerns with respect to OFDM signals inparticular. That is, OFDM signals are very sensitive to nonlinearintermodulation, especially composite triple beat (CTB). Second-ordernonlinear products are out-of-band and are typically filtered. However,most third-order nonlinear products are located in-band, and causeproblems by overlapping with existing carriers.

TABLE 1 CM minimum CNR performance in AWGN channel CNR (dB) up toConstellation (QAM) CNR (dB) up to 1 GHz 1.0-1.218 GHz 4096 41 41.5 204837.0 37.5 1024 34.0 34.0 512 30.5 30.5 256 27.0 27.0 128 24.0 24.0 6421.0 21.0 16 15.0 15.0

TABLE 2 CMTS minimum CNR performance in AWGN channel Constellation (QAM)CNR (dB) 4096 43.0 2048 39.0 1024 35.5 512 32.5 256 29.0 128 26.0 6423.0 32 20.0 16 17.0 8 14.0 QPSK 11.0

Accordingly, the link loss and the analog linear distortionssignificantly limit the achievable link budget of the conventional HFCnetwork. The effect on the achievable link budget is even morepronounced with respect to high-order modulation formats, which target ahigh data rate. Conventional analog optics technology is unable to keepup with the increasing data demand on legacy HFC networks. Replacingsuch legacy HFC networks, however, would be very expensive, and thusimpractical.

BRIEF SUMMARY

In an embodiment, an analog signal processor includes a sampling unitconfigured to (i) filter, in the frequency domain, a received timedomain analog signal into a low-frequency end of a correspondingfrequency spectrum, (ii) sample the filtered analog signal at afrequency substantially higher than the low-frequency end, and (iii)spread quantization noise over an expanded Nyquist zone of thecorresponding frequency spectrum. The processor further includes a noiseshaping unit configured to shape the spread quantization noise out ofthe low-frequency end of the corresponding frequency spectrum such thatthe filtered analog signal and the shaped quantization noise aresubstantially separated in the frequency domain, and a quantization unitconfigured to apply delta-sigma modulation to the filtered analog signalusing at least one quantization bit and output a digitized bit streamthat substantially follows the amplitude of the received time domainanalog signal.

In an embodiment, a hybrid fiber coaxial (HFC) network is provided. Thenetwork includes an optical hub configured to transmit a digitized bitstream over a digital optical link, a fiber node configured to receivethe digitized bit stream over the digital optical link and convert thereceived digitized bit stream into a delta-sigma demodulated analogsignal, and at least one end user configured to receive the delta-sigmademodulated analog signal from the fiber node.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the presentdisclosure will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein:

FIG. 1 is a schematic illustration of a conventional HFC network.

FIGS. 2A-2B are graphical illustrations depicting respective operatingprinciples of a conventional sampling process 200 compared with anexemplary modulation process.

FIG. 3 is a graphical illustration depicting an operating principle of ademodulation process for the modulated digitized output signal depictedin FIG. 2B, according to an embodiment.

FIGS. 4A-B are schematic illustrations of an exemplary HFC networkutilizing the delta-sigma modulation process depicted in FIG. 2B, andthe delta-sigma demodulation process depicted in FIG. 3.

FIGS. 5A-B are schematic illustrations of an exemplary digitizeddistributed network utilizing the delta-sigma modulation processdepicted in FIG. 2B, and the delta-sigma demodulation process depictedin FIG. 3.

FIGS. 6A-B are schematic illustrations of an exemplary radio frequencyover glass network utilizing the delta-sigma modulation process depictedin FIG. 2B, and the delta-sigma demodulation process depicted in FIG. 3.

Unless otherwise indicated, the drawings provided herein are meant toillustrate features of embodiments of this disclosure. These featuresare believed to be applicable in a wide variety of systems including oneor more embodiments of this disclosure. As such, the drawings are notmeant to include all conventional features known by those of ordinaryskill in the art to be required for the practice of the embodimentsdisclosed herein.

DETAILED DESCRIPTION

In the following specification and the claims, reference will be made toa number of terms, which shall be defined to have the followingmeanings.

The singular forms “a,” “an,” and “the” include plural references unlessthe context clearly dictates otherwise.

“Optional” or “optionally” means that the subsequently described eventor circumstance may or may not occur, and that the description includesinstances where the event occurs and instances where it does not.

Approximating language, as used herein throughout the specification andclaims, may be applied to modify any quantitative representation thatcould permissibly vary without resulting in a change in the basicfunction to which it is related. Accordingly, a value modified by a termor terms, such as “about,” “approximately,” and “substantially,” are notto be limited to the precise value specified. In at least someinstances, the approximating language may correspond to the precision ofan instrument for measuring the value. Here and throughout thespecification and claims, range limitations may be combined and/orinterchanged; such ranges are identified and include all the sub-rangescontained therein unless context or language indicates otherwise.

According to the embodiments described herein, a digital optical networkimplements a digital optical link over a digitized distributed network,or utilizing a digitized analog signal over the conventional HFCnetwork. The digital optical network according to the present systemsand methods is less affected by link loss, and also realizes a highertolerance to nonlinear noise from the laser (e.g., of the headend/hub)or the fiber itself when the optical power is above the sensitivity ofthe receiver (e.g., of an end user). The present digital optical networkis therefore advantageously able to realize transmission over longerdistances, support wavelengths per fiber, and effectively eliminateoptical noise contribution to CNR. Moreover, according to theadvantageous techniques described herein, the CMTS and respective CMsmay operate at higher orders of modulation format.

In the exemplary embodiments, optical digital transmission isaccomplished utilizing delta-sigma modulation and demodulation. Keysteps in the optical digital transmission process includeanalog-to-digital (A/D) and digital-to-analog (D/A) conversion. The A/Dconversion (ADC) and D/A conversion (DAC) subprocesses involve twoimportant factors: (1) sampling rate; and (2) bit resolution. Theminimum sampling rate is generally governed according to the NyquistSampling Theorem, whereas the bit resolution it important fordetermining the quantization noise. In some of the embodiments describedbelow, a DOCSIS digitization scheme, utilizing delta-sigma modulationand demodulation, is applied to variations of a conventional HFC networkand implements one or more of (i) oversampling, (ii) decimationfiltering, and (iii) quantization noise shaping, to achieve ultra-highresolution and excellent antialiasing filtering. The present embodimentsare therefore of particular advantageous use in audio applications,precision temperature measurements, and weighing scales.

The present systems and methods are further capable of implementinglow-pass filtering that does not demand the processing latencyexperienced in conventional HFC networks. Furthermore, the presentoptical digital transmission systems and networks realize even lowerlatencies than those experienced utilizing conventional ADC/DACapproaches. Low latency is a particularly critical factor in virtualreality and immersive applications that networks of the future will haveto support. By leveraging frequency selective digitization, the presentembodiments are even further able to advantageously reduce the amount ofdata required to represent the analog spectrum, such as the analog cablesignal of HFC network 100, FIG. 1, above.

FIGS. 2A-2B are graphical illustrations depicting respective operatingprinciples of a conventional sampling process 200 compared with anexemplary modulation process 202, according to an embodiment. Process200 depicts the operation of a conventional Nyquist-Shannon sampling ADCfor an analog signal 204 (shown the time domain). In the exemplaryembodiment, process 200 bandwidth-limits analog signal 204 in thecorresponding frequency domain (e.g., using a low-pass filter 206, atfrequency f_(B)). In the example shown in FIG. 2A, quantization noise208 is uncorrelated with the frequency of the input signal, and isspread evenly over the Nyquist bandwidth f_(S)/2. Process 200 performsNyquist sampling 210 of analog signal 204 (i.e., at the Nyquistfrequency), and quantizes each sample by multiple quantization bits toproduce multi-bit quantization signal 212.

Since the quantization noise of a Nyquist ADC is approximately Gaussian,as well as uniformly spread over the Nyquist zone, a very large numberof quantization bits are needed to ensure the signal-to-noise ratio(SNR) (e.g., CNR or MER) of the resulting digitized signals 212. Such alarge number of required quantization bits leads to very highrequirements for the effective number of bits (ENOB), while alsoproducing a low spectral efficiency and a data rate bottleneck. That is,according to the prior art techniques, a narrow band analog signal canconsume tremendous transmission bandwidth after digitization, due to thelarge number of quantization bits for each sample.

These drawbacks of conventional sampling techniques are solved accordingto exemplary modulation process 202. As depicted in FIG. 2B, inexemplary modulation process 202, a processor 214 of an A/D converter(not shown in FIG. 2B) applies delta-sigma modulation to exploit anoversampling ADC that utilizes one or two quantization bits on an inputsignal 216 to generate an output signal 218. In some embodiments, outputsignal 218 is binary (e.g., one-bit quantization). In other embodiments,output signal 218 is a PAM4 output signal (e.g., two-bit quantization).

More particularly, modulation process 202 implements an oversamplingsubprocess 220, a noise shaping subprocess 222, and a quantizationsubprocess 224. In oversampling subprocess 220, modulation process 202samples analog input signal 216 (e.g., a DOCSIS RF signal) at a highfrequency, and spreads the quantization noise over an expanded Nyquistzone 226. Modulation process 202 then implements noise shapingsubprocess 222 to push the quantization noise out of the signal band. Inthe example depicted in FIG. 2B, a low-pass delta-sigma modulator 228places analog signal 216 in the low-frequency end of the spectrum, and anoise transfer function 230 functions as a high-pass filter to push thequantization noise out of the signal band to the high frequency end,such that analog signal 216 is separated from the noise in the frequencydomain. The delta-sigma modulation technique of modulation process 202outputs binary (e.g., on/off key (OOK)) signal 218 (1) or non-binarysignal 218 (2) (e.g., PAM4 (pulse-amplitude-modulation having fouramplitude levels)), depending on one-bit or two-bit quantization, andhaving a baud rate equal to the oversampling ADC of the subprocess 220.Accordingly, the resulting output binary or non-binary signal 218generally follows the amplitude of analog input signal 216 in an averagesense.

According to the advantageous technique of modulation process 202, theoutput produced using the present delta-sigma modulation techniquesrepresents a high data rate bit stream (e.g., output 218), having anamplitude that generally tracks with the amplitude of the input analogsignal (e.g., input signal 216) after a weighted moving average, forexample. In the exemplary embodiment, an averaging process implementslow-pass filtering, and is thereby capable of smoothing out the highfrequency oscillation of the output digitized bit stream. The use oflow-pass filtering further advantageously allows for easier and morereliable retrieval, i.e., modulation, of the original analog signal fromthe output digitized bit stream, as described below with respect to FIG.3.

FIG. 3 is a graphical illustration depicting an operating principle of ademodulation process 300 for the modulated digitized output signal 218,FIG. 2B, above. More specifically, in demodulation process 300, aprocessor 302 implements delta-sigma demodulation to retrieve an analogsignal 304 from digitized bit stream 218, FIG. 2B, using a low-passfilter 306. This advantageous technique is significantly simpler incomparison to the conventional Nyquist DAC, which reads the quantizationbits of each sample, and converts the read quantization bits to anappropriate output level. A frequency domain diagram 308 illustrates theadvantages of the present delta-sigma operating principle, in thefrequency domain, over the more laborious conventional Nyquistdemodulation techniques. That is, low-pass filter 306 effectivelyeliminates the out-of-band noise and filters retrieved analog signal 304at the low frequency end. In this example, as illustrated in FIG. 3,retrieved analog signal 304 has an uneven noise floor 310 due to noiseshaping.

FIGS. 4A-B are schematic illustrations of an exemplary digitized HFCnetwork 400 utilizing modulation process 202, FIG. 2B, and demodulationprocess 300, FIG. 3. Digitized HFC network 400 is similar to HFC network100 in overall structure, except that digitized HFC network 400 isconfigured to implement delta-sigma modulation and demodulation insteadof the conventional A/D and D/A conversion techniques. Specifically, HFCnetwork 400 includes a headend 402, a hub 404, a fiber node 406, endusers/subscribers 408, and at least one optical fiber 410 connecting thelink between headend 402, hub 404, and fiber node 406. Optical fiber 410is also configured to carry digitized bit streams of the downstreamand/or upstream optical signals. A plurality of coaxial cables 412connect fiber node 406 to respective end users 408, and carry the analogelectrical signals therebetween. Digitized HFC network 400 optionallyimplements amplifiers 414 along coaxial cables 412.

In some embodiments, both of the digitized upstream and downstreamoptical signals are transmitted along the same optical fiber 410. Insuch instances, hub 404 includes an optical multiplexer/demultiplexer416 for respectively combining/splitting the downstream and upstreamoptical signals, and fiber node 406 similarly includes an opticalmultiplexer/demultiplexer 418. Multiplexers/demultiplexers 416, 418 maybe passive devices, such as diplexers, or active configuration units. Inother embodiments, the upstream and downstream signals are transmittedalong separate fibers, and multiplexing is optional (e.g., wheremultiple optical signals are transmitted in the same direction).

FIG. 4B illustrates an exemplary architecture 420 for implementing thedelta-sigma modulation and demodulation processes of digitized HFCnetwork 400. In operation of architecture 420, a downstream analogsignal (e.g., analog signal 216, FIG. 2B) from a CMTS 422 of headend402/hub 404 is converted into a digital signal by a downstreamdelta-sigma modulator 424 (e.g., using modulation process 202, FIG. 2B)for analog signal digitization. In the exemplary embodiment, thedownstream analog signal is an analog DOCSIS RF signal from a broadcastservice of CMTS 422, or may constitute edge QAM technology or aconverged cable access platform (CCAP). A bit stream (e.g., output 218,FIG. 2B) generated by downstream modulator 424 drives a downstreamdigital optical transmitter 426 to transmit the downstream digitized bitstream over optical fiber 410 to be received by a downstream digitaloptical receiver 428 of fiber node 406.

At fiber node 406, an upstream delta-sigma demodulator 430 converts(e.g., by demodulation process 300, FIG. 3) the downstream electricaldigital bit stream from downstream delta-sigma modulator 424 back intoanalog form, where this demodulated downstream analog signal may befurther transmitted throughout an existing HFC cable infrastructure,such as over coaxial cables 412, amplifiers 414, and optional taps 432.

In further operation of digitized HFC network 400, upstreamtransmissions are accomplished similarly to the downstreamtransmissions, but in reverse. That is, fiber node 406 receives ananalog RF signal from one or more end users 408. An upstream delta-sigmamodulator 434 converts the upstream analog signal into a digitalupstream bit stream, which drives an upstream digital opticaltransmitter 436 of fiber node 406 to transmit the upstream digitized bitstream over optical fiber 410, to be received by an upstream digitaloptical receiver 438 of hub 404. An upstream delta-sigma demodulator 440converts the upstream electrical digital bit stream into analog form,which may then be received by CMTS 422.

As described above, for upstream transmissions, a different opticalwavelength from the downstream transmission may be used. Alternatively,the downstream and upstream digitized bit streams may be separatelytransmitted over separate optical fibers 410 _(DS) and 410 _(US),respectively. In the alternative embodiments, an electrical diplexer 442and or optical multiplexers/demultiplexers (e.g., elements 416, 418,FIG. 4A) may be utilized where node aggregation and/or node splitting isdesired. The present embodiments are therefore of particular advantageto fiber-starved network environments faced by many present-day cableoperators, where more limited conventional node aggregation andsplitting techniques are commonly implemented to maximize fiberutilization.

By rendering the delta-sigma modulation and demodulation processescomplementary (or the same) in both the downstream and upstreamdirections, the present techniques may be further advantageouslydeployed within existing legacy HFC networks, and without requiringsignificant hardware modifications to the CMTS in the headend/hub, or tothe existing infrastructure between the fiber node and end users (i.e.,electrical amplifiers, taps, etc.). In the exemplary embodimentillustrated in FIGS. 4A-4B, the optical connection between the hub andthe fiber node is upgraded to a digital optical link. Through thisdigital optical link, digitized HFC network 400 is thereforeadvantageously capable of utilizing several different optical transporttechnologies, such as direct optical detection or coherent opticaldetection, depending on the requirement of oversampling rate and SNR forthe various transmission conditions (e.g., legacy fiber, distance, etc.)and resulting link capacity. Through these advantageous techniques, thepresent systems and methods are thus able to achieve significantlylonger transmission distances through use of the high-performance,delta-sigma modulation-based digital transmission.

At present, transport in the cable environment is asymmetric.Accordingly, the requirements for HFC systems that implement the presentdelta-sigma modulation techniques may also be applied asymmetrically.According to the delta-sigma modulation techniques described hereinthough, only the transmitter side experiences increased complexity tothe oversampling subprocesses. In contrast, no such complexity isrequired on the receiver side. That is, implementation costs at thereceiver side will be minimal. However, the asymmetry of conventionalHFC networks nevertheless allows implementation costs on the transmitterside to be significantly reduced as well. For example, some DOCSIS 3.1implementations utilize a high-split scenario, such as 1.2 GHzdownstream/200 MHz upstream. Accordingly, the costs of transmittingupstream will still be reduced in comparison with costs of transmittingdownstream, since the upstream bandwidth is a fraction of the downstreambandwidth. Furthermore, since many end users do not fully utilize theavailable upstream transport, the sampling needs from a customerperspective might be even lower in practice, and therefore the resultingtransmitter implementation costs on the customer side as well.

Additionally, the digital optical link of the upgraded node, accordingto the embodiments illustrated in FIGS. 4A-B, achieve significantlyimproved reliability as compared to conventional techniques that areintended to support higher DOCSIS performance levels. That is, thedelta-sigma modulation/demodulation techniques of the presentembodiments will have superior reliability over conventionalremote-CMTS, remote-PHY, and A/D-D/A digitization approaches. Thedelta-sigma modulation and demodulation processes described hereintherefore have particular applicability to support heterogeneous serviceenvironments that include wireless backhaul and business connectionsaccording to end user requirements, while greatly simplifying theoperational complexity for all end users.

FIGS. 5A-B are schematic illustrations of an exemplary digitizeddistributed network 500 utilizing modulation process 202, FIG. 2B, anddemodulation process 300, FIG. 3. As shown in FIG. 5A, distributednetwork 500 is structurally similar to digitized HFC network 400, andincludes a headend 502, a hub 504, a fiber node 506, endusers/subscribers 508, at least one optical fiber 510, a plurality ofcoaxial cables 512, and optional amplifiers 514. Distributed network 500differs though, from digitized HFC network 400 in operation, asexplained further below with respect to FIG. 5B.

FIG. 5B illustrates an exemplary distributed architecture 516 forimplementing the delta-sigma modulation and demodulation processes ofdistributed network 500. Operation of distributed architecture 516differs from the operation of architecture 420, FIG. 4, in thatdistributed architecture 516 distributes the PHY layer into the HFCnetwork. That is, distributed architecture 516 distributes the PHY layerto fiber node 506 (or the PHY shelf), thereby effectively removing thePHY from a CMTS 518 (i.e., the CCAP Core), for example, thereby furtherrendering it possible to eliminate the need for an analog laser (notshown) in the headend 502/hub 504. In this embodiment, CMTS 518 is thusfunctionally converted to digital fiber Ethernet link (e.g., a networkaggregation layer for an optical Ethernet or passive optical network(PON)), and optical fiber 510 functionally serves as an optical Ethernetdigital fiber.

At fiber node 506, a digital optical transceiver 520 receives thedigital signals from CMTS 518, at a downstream distributed MAC/PHY layer522 for conversion, by a downstream delta-sigma demodulator 524, to ananalog signal. Similarly, an upstream delta-sigma modulator convertsanalog signals from end users 508 into digitize signals for an upstreamdistributed MAC/PHY layer 528 to provide to digital optical transceiver520 for upstream transport over fiber 510. Similar to architecture 420,FIG. 4, distributed architecture 516 may further include a diplexer 530and at least one tap 532. In this example, distributed architecture 516advantageously utilizes downstream delta-sigma demodulator 524 as a D/Aconverter, and upstream delta-sigma modulator 526 as an A/D converter.Therefore, the delta-sigma modulation and demodulation techniques ofFIGS. 5A-B may be fully implemented in both the upstream and downstreamdirections, respectively.

According to this embodiment, a low-cost demodulation process isprovided. The implementation thereof achieves an ultra-high resolutionfor RF signal conversion, and is capable of utilizing either direct orcoherent detection technologies using the optical connection between theheadend/hub and fiber node. Through the economic simplification ofdistributed architecture 516, distributed network 500 requires only onedelta-sigma modulator/demodulator pair at fiber node 506 forRF-to-digital conversion.

FIGS. 6A-B are schematic illustrations of an exemplary radio frequencyover glass (RFoG) network 600 utilizing modulation process 202, FIG. 2B,and demodulation process 300, FIG. 3. As shown in FIG. 6A, RFoG network600 is structurally similar to digitized HFC network 400, and includes aheadend 602, a hub 604, a fiber node 606, end users/subscribers 608, atleast one optical fiber 610, a plurality of coaxial cables 612, andoptional amplifiers 614. RFoG network 600 differs though, from digitizedHFC network 400, in that RFoG analog optics technology transmits RF overfiber, instead of coaxial cable, to a terminating unit (e.g., an opticalnetwork unit (ONU) or an optical network terminal (ONT), notindividually shown) deployed at the respective customer premises of endusers 608.

FIG. 6B illustrates an exemplary RFoG architecture 616 for implementingthe delta-sigma modulation and demodulation processes of RFoG network600. RFoG architecture 616 is similar to architecture 420, FIG. 4, andincludes a CMTS 618, a downstream delta-sigma modulator 620, adownstream digital optical transmitter 622, a hub diplexer 624 (ormultiplexer/demultiplexer), a fiber node diplexer 626 (ormultiplexer/demultiplexer), a downstream digital optical receiver 628, adownstream delta-sigma demodulator 630, an upstream delta-sigmamodulator 632, an upstream digital optical transmitter 634, an upstreamdigital optical receiver 636 of hub 604, and an upstream delta-sigmademodulator 638. In the exemplary embodiment, RFoG architecture 616further includes at least one optical splitter 640 disposed alongoptical fiber 610. Downstream delta-sigma demodulator 630 and upstreamdelta-sigma modulator 632 communicate with a customer premises equipment(CPE) 642 of at least one end user 608.

According to the advantageous embodiments illustrated in FIGS. 6A-B, asignificant improvement to the transmission performance of the digitallink of RFoG network 600 is achieved by introducing delta-sigmamodulation and demodulation processes at both the headend/hub and thecustomer premises/end users, thereby effectively replacing opticalconnection with digital transmissions. The architecture and operation ofRFoG network 600 is particularly advantageous to customer users havingexisting home coaxial wiring and/or CPEs; implementation of RFoG network600 requires no hardware changes to such existing infrastructure.Furthermore, the digital fiber deep architecture of RFoG network 600further allows the delivered data rate to be increased to end users 608.Where splitter 640 is implemented, the splitting ratio may also befurther increased due to the higher power budget margin achievable fromsuch digital transmission links.

According to the advantageous systems and methods described above,efficient digitization techniques may be employed over conventional HFCin RFoG networks to significantly expand transport capabilities ofexisting fiber strands, and without requiring significant hardwaremodification or costs. The systems and methods described herein utilizeexisting fiber infrastructures to increase the capacity of such existinginfrastructures, but without increasing complexity at the receiver side.The present embodiments also advantageously utilize existing networktransmission asymmetry to further reduce complexity at the transmitterside. The present systems and methods thus significantly extend the lifeof existing fiber infrastructures, and also more efficiently useexisting optical wavelengths. Through the techniques described herein, afiber communication network will realize increased scalability, therebyallowing the network to flexibly grow according to increasing demandfrom cable subscribers.

Exemplary embodiments of analog digitization systems and methods aredescribed above in detail. The systems and methods of this disclosurethough, are not limited to only the specific embodiments describedherein, but rather, the components and/or steps of their implementationmay be utilized independently and separately from other componentsand/or steps described herein. Additionally, the exemplary embodimentscan be implemented and utilized in connection with other access networksutilizing fiber and coaxial transmission. That is, the delta-sigmamodulation techniques herein are described with respect to digitizationinterfaces for centralized HFC networks, distributed HFC networks, andRFoG networks, but the person of ordinary skill in the art, afterreading and comprehending the present description and accompanyingdrawings, will appreciate that the present embodiments may be furtherapplied to other network applications.

This written description uses examples to disclose the embodiments,including the best mode, and also to enable any person skilled in theart to practice the embodiments, including making and using any devicesor systems and performing any incorporated methods. The patentable scopeof the disclosure is defined by the claims, and may include otherexamples that occur to those skilled in the art. Such other examples areintended to be within the scope of the claims if they have structuralelements that do not differ from the literal language of the claims, orif they include equivalent structural elements with insubstantialdifferences from the literal language of the claims. Although specificfeatures of various embodiments of the disclosure may be shown in somedrawings and not in others, this is for convenience only. In accordancewith the principles of the disclosure, a particular feature shown in adrawing may be referenced and/or claimed in combination with features ofthe other drawings.

Some embodiments involve the use of one or more electronic or computingdevices. Such devices typically include a processor or controller, suchas a general purpose central processing unit (CPU), a graphicsprocessing unit (GPU), a microcontroller, a reduced instruction setcomputer (RISC) processor, an application specific integrated circuit(ASIC), a programmable logic circuit (PLC), a field programmable gatearray (FPGA), a DSP device, and/or any other circuit or processorcapable of executing the functions described herein. The processesdescribed herein may be encoded as executable instructions embodied in acomputer readable medium, including, without limitation, a storagedevice and/or a memory device. Such instructions, when executed by aprocessor, cause the processor to perform at least a portion of themethods described herein. The above examples are exemplary only, andthus are not intended to limit in any way the definition and/or meaningof the term “processor.”

This written description uses examples to disclose the embodiments,including the best mode, and also to enable any person skilled in theart to practice the embodiments, including making and using any devicesor systems and performing any incorporated methods. The patentable scopeof the disclosure is defined by the claims, and may include otherexamples that occur to those skilled in the art. Such other examples areintended to be within the scope of the claims if they have structuralelements that do not differ from the literal language of the claims, orif they include equivalent structural elements with insubstantialdifferences from the literal language of the claims.

What is claimed is:
 1. A transmitting signal processor in operablecommunication with a first end of a digital transport medium,comprising: an input portion configured to receive a digitized radiofrequency (RF) signal including quantization noise over an expandedNyquist zone of a frequency spectrum corresponding to the digitized RFsignal; a noise shaper configured to implement a noise transfer function(NTF) to shape the quantization noise out of a low-frequency end of thecorresponding frequency spectrum to generate a shaped signal such thatthe received digitized RF signal and the shaped quantization noise aresubstantially separated in the frequency domain, wherein the NTF isconfigured to correspond with a filter function of a receiving processordisposed at a second end of the digital transport medium opposing thefirst end; and a quantizer configured to apply delta-sigma modulation tothe shaped signal using at least one quantization bit, and output to thedigital transport medium a digitized bit stream that substantiallyfollows the amplitude of the received digitized RF signal.
 2. Thetransmitting processor of claim 1, wherein the received digitized RFsignal is a data over cable service interface specification (DOCSIS) RFsignal.
 3. The transmitting processor of claim 1, wherein thedelta-sigma modulation uses a one-bit quantization.
 4. The transmittingprocessor of claim 3, wherein the output digitized bit stream comprisesa binary signal.
 5. The transmitting processor of claim 1, wherein thedelta-sigma modulation uses a two-bit quantization.
 6. The transmittingprocessor of claim 5, wherein the output digitized bit stream comprisesa PAM4 signal.
 7. The transmitting processor of claim 1, furthercomprising (i) a transmitter filter configured to filter a time domainanalog signal in the frequency domain to produce a filtered frequencydomain signal, and (ii) a sampler configured to sample the filteredfrequency domain signal at a frequency substantially higher than thelow-frequency end to provide the digitized RF signal to the inputportion.